Propellers for water craft



Sept. 27, 1966 r R; E. STARK PROPELLERS FOR WATER CRAFT 5 Sheets-Sheet 1 Filed 'Aug. .19, 1965 Sept. 27,1966 I R. E. STARK 3,275,082

PROPELLERS FOR WATER CRAFT Filed Aug. 19, L965 5 Sheets-Sheet 2 7 INVENTOR. .3 der'? S-Mrk Sept. 27, 1966 v R. E. STARK 3,275,082

PROPELLERS FOR WATER CRAFT I Fiied Aug. 19, 1965 s Sheets-Sheet s INVENTOR Ruben ET BY ill-M United States Patent 3,275,082 PROPELLERS FOR WATER CRAFT Robert E. Stark, 176 Crestwood Drive, Avon Lake, Ohio Filed Aug. 19, 1965, Ser. No. 481,000 9 Claims. '(Cl. 170-1605) This relates to propellers for water craft and more particularly to a propeller in which the pitch it automatically adjusted according to the speed of the engine, the speed of the boat and the load.

As is well known to those versed in the art, marine propellers are usually designed so that they operate most etliciently at one particular speed which is usually the cruising speed. The result is that at all other speeds it lacks efficiency and only attains its maximum efficiency when driven at the rated speed. Such a propeller must be driven at a slower speed when a reduction in the speed of the craft is desired. This is undesirable because when the engine is driven at a low speed the engine cooling system causes the engine to become hot, carbon up, foul the spark plugs, and reduce engine life.

Although propellers have been designed with a socalled adjustable pitch, which was supposed to overcome the above noted deficiencies, these are not entirely satisfactory. On reason was because the blades as a whole were turned on their radial axis to change the pitch and at only one adjustment were they capable of operating at true pitch; all the other positions were a compromise. True pitch is attained where every blade section taken along an arc, the focus of which is on the axis of rotation, theoretically advances the same distance per revolution because of the pitch angle of the blade section. Thus, all points on the blade tend to move forward the same distance for each revolution. In such a propeller the pitch angle can be calculated at any desired distance out from the axis of rotation. As the radius approaches infinity, the pitch angle approaches zero, and, at the axis where the radius is zero, the pitch angle is 90. .When propellers are designed with blades which adjust the pitch by turning the whole blade, they are of true or approximately true pitch for only one adjusted position and are no longer true pitch for all of the other adustments, resulting in a deterioration of efficiency at another speeds.

The fixed blade propellers deliver maxium horsepower from the engine under only one load condition. Thus, in a small boat a major change in delivered horsepower will be experienced depending on the number of passengers carried or the load changes which occur when towing an object such as another boat or a water skier or upon executing turning maneuvers. The use of such a propeller can also result in engine over-speed at full throttle under low load conditions and is not desirable for slow speeds, such as trolling because the low speed results in increased engine vibration, frequent stalling of the engine, and, with the loss of loading, carbon deposits and spark plug fouling occur as previously mentioned.

In addition to the above, which is a common defect in all variable pitch propellers heretofore, there are certain other disadvantages specific to the particular type of propellers among which the following may be enumerated.

Propellers which may be adjusted manually by a remote means have been proposed where the adjustment is obtained by mechanical or hydraulic means controlled from a remote location. This requires additional mechanism which is expensive to manufacture, difficult to maintain because water seals fail in time, and to service, because they are complicated.

In addition, self-adjusting propellers are common which use blade area, cams, springs or weights in combination, to automatically change the pitch with changes in rpm. and load. These are also expensive to manufacture, sub- "ice ject to considerable servicing and deteriorate rapidly.

They are also subject to rapid deterioration in salt water.

Then there is the manually adjustable pitch propeller wherein the propeller rotation must be stopped before the angular adjustment of the blade can be made. These propellers :are relatively inexpensive as compared with the other types and require less service, but are decidedly inconvenient when it comes to making the adjustment to change the pitch. In an outboard motor this is not too serious a problem because the engine can be tilted on the transom and the adjustment made relatively quickly, but with the larger water craft it is very difficult to adjust the propellers because they are usually submerged in the water at all normal times.

The present invention contemplates a propeller which may be made of a flexible plastic and wherein the pitch angle of the blades is automatically changed by a deflecting or twisting of the blade, from. its at rest position, during the various speeds and under conditions of variable loading. This enables a propeller to be made which is extremely simplified in construction as compared with the other variable pitch propellers. They can be made in one piece and have no moving parts except the blades themselves which move by flexing only.

Another advantage is that it can be made at a very low cost and by methods of manufacture heretofore not practical in the other type propellers.

One of the most important and desirable features, however, is the fact that although a variable pitch propeller is realized, it is a materially closer approximation to a true pitch propeller at :all changes in pitch, due to speed and loading, since the root of the blade remains fixed and the flexing or bending is progressively larger proceeding along the blade to the outer edge.

Still other advantages reside in the fact that the pitch changes automatically with changes in load, requires no servicing at all, maintains high reliability, is highly resistant to corrosion of all kinds and may be made at a very low cost.

Still other advantages of the invention and the invention itself will become more apparent from the following description of some embodiments thereof, which description is illustrated by the accompanying drawings and forms a part of this specification.

In the drawings:

FIG. 1 is a fragmentary top plan view of a propeller made according to the invention;

FIG. 2 is an enlarged side elevational view thereof;

FIG. 3 is a view at to FIG. 2;

FIGS. 4 and 5 are views similar to FIGS. 2 and 3 of a modified form; and

FIGS. 6 and 7 are similar views of still another form.

Briefly, the propeller contemplates a single unit'having one or more blades made of a suitable plastic and having a predetermined pitch at rest and wherein the plastic has cont-rolled flexibility designed into the parts and with certain parts weighted so that the centrifugal forces and the load on the blade or blades automatically causes an adjustment of the pitch for optimum efficiency at all speeds within the range for which it is designed.

Referring to the drawings, throughout which like parts are designated by like reference characters and particu larly to FIGS. 1 to 3 inclusive, there is provided the usual propeller hub 10 having a tapered bore 11 for assembly on the usual propeller shaft, not shown. The blades project radially from the hub, the pitch of which may vary from the root toward the end of the blade according to the usual formula for a true pitch propeller for cruising at low speeds.

It is also contemplated that the pitch could become progressively less from the hub end of the blade toward the tip, at zero r.p.m., and become constant throughout 7 its length as the blade approaches cruising speed.

As can best be seen from FIG. 1, as the blade extends outward it widens substantially symmetrically on'each Side of its radial axis X. The blade tip is generally of helicoidal form such that the outer trailing edge. at the tip 12 is at a greater radial distance from the hub axis than the leading edge 14 to thus provide a larger area on the trailing side of the radial axis, the terminating end being an acute angle. At high loads, this larger surface area behind the radial axis causes a decrease in the pitch. As can be seen from FIG. 2, the angle a of the blade at the root is maximum and the angle b at the tip minimum.

A weighted fin 15 is provided on the low pressure side of the blade, extending from the intersection of the leading edge 14 and the end of the blade to the trailing edge 16 spaced from the tip 12. The fin shape is preferably that of a curve having a radius the axis of which may be the axis of the propeller hub." It is preferred that the fin have a reasonably sharp leading edge and increase in thickness symmetrically on each side of the semi-circular center line, for a short distance and then decrease in thickness toward their trailing edge, the purpose being to increase the rigidity and to streamline this part of the blade to reduce the tendency to cause undue turbulence. It is pointed out that the fin could be the same thickness throughout its length.

Also, as can best be seen from FIG. 2, the leading edge of the fin merges with the leading edge of the propeller blade and gradually increases in width toward the trailing edge 18. The trailing edge is sharp with the midsection curved inwardly at 19 from the outer edge and then outward at 20 to the bottom edge with a fishtail effect. A weight 17 may be incorporated in the plastic at the time of molding and may be of the general conformation shown in FIG. 2.

It will be appreciated that the above features of the design are along the lines to best prevent undue turbulence but that the basic features of the design about to be described could depart from the specific design materially and still takeadvantage of the invention. a

To better understand the basic features of the invention and manner of the operation,'the following is advanced as the mode of its operation and is believed to be a correct explanation thereof. Should it subsequently appear that the operation is the result of a difierent mode, it is not the intention that the invention be limited thereby. Each of'the blades as a whole should be considered as dividedinto two sections, FIG. 1, by a radial axis X. Each section is designed with a center of mass at L and T. The centrifugalforces on these masses at a certain speed may be represented by the vectors L0 and TU. These forces can be resolved into vectors parallel to the radial axis, LQ and TW, and vectors perpendicular to the radial axis, LP and TV. Obviously the length of all these vectors will vary with r.p.m. In FIG. 2 the vectors LP and TV show that these forces act through moment arms RB and RC respectively, to cause a twisting of the blade, as

.the r.p.m. increases, to decrease the pitch of the blade.

This is a characteristic common to essentially all blades .and one which has a definite effect on the blade efliciency at the higher r.p.m.s and can result in metal fatigue and failure in time. With a blade made of plastic, the fatigue is no problem but as in other blades it could result in a smaller pitch angle.

Means is provided to counteract this inherent defect and at the same time usually cause pitch increase with increase in r.p.m. This is efiected by the fin.

The fin 15 is so designed that the center of mass is at v the point P and the centrifugal force, represented by the vector FG, FIG. 1, can be resolved into vectors FJ parallel to the radial axis and FH perpendicular to the radial axis. FH,-as shown in FIG. 2, acts through moment arm RD, as shown by the arrow, which increases the pitch of 4 the blade with increase in r.p.m. Hence, the pitch angle of the blade will increase with r.p.m. if FH RD (LPXRB) (TVXRC) The centrifugal force on the mass of the attached fin which is parallel .to the radial axis is represented by F] (FIGS. 1 and 3). This force acting on the fin is opposed by the restraining force FK (FIG. 3), which is inherent in the rigidity of the structure, and the resultant vector FM is opposed "by water pressure represented by vector EG. Hence the deflection that is normally'experienced in a flexible blade, due to water pressure, is overcome.

The, bending of the blade is also resisted by the passage of the fin in a circular path through. the Water; As the r.p.m. increases and the tendency of the blade is to bend, this effect is overcome by the relative movement between the fin and the water on each side of the The higher .the r.p.m. the greater the resistance to the bending.

In FIGS. 4 and 5 there is shown anothcr'embodiment of the, invention wherein the blade 26 extends from the hub 10 inia similar manner to that .of FIGS. l to 3 inclusive. In this instance,.however, the fin.27, which is integral, with the blade atits' outer extremity, is'formed so that the water slipping oifthe tip of the blade, which bends toward the low pressure side,'will cause the pitch change to increase the pitch with increase in r.p.m. In

this instance, one design contemplates that the .fin start at 28, spaced from the leading edge and rises to height rapidly at about the center 29 of the blade and terminates in a sharp point 30 at the trailing edge, as best seen in FIG. 4. As shown in FIG. 5, the fin does not extend from the blade normal to the axis of the hub but slants outwardly from the points of attachment to the blade in a shallow S curve.

Still another modification depicted in FIGS. 6 and 7 contemplates a design where the pitch change is accomplished largely by centrifugal'force. As shown in FIG. 6

the blade extends outwardly from the hub 10 and laterally symmetrically from the center line X. It has the usual pitch change from the root 30 to the tip 31, which is designed for low r.p.m. Near the tip of the blade,. and on the blade axis, a weight 32 isincorporated in the. blade.

At the 'root of the blade, theflexi-bility is increased by the angle at the root is greater and the centrifugal force causes the blade to tip from the lesser pitch to'the greater pitch of the root. Although the zone 33 isillustrated as being of limited length, it will be appreciated that it may be longer and of a design such that the blade does not rotate about its axis for equal degrees throughout its length as did the previous propeller blades, but that the change in pitch angle is less per r.p.m. near the, tip and for each increment of length toward the hub, from the tip toward the hub, thus enabling .a' substantially true pitch propeller blade to be obtained for each speed of the propeller.

From the foregoing, and as previously mentioned, it is apparent that the blades maybe made from-the various types of plastics, such as polyvinylchloride, polyethylene, Delrin, Lexan and epoxy resins. They may be manufactured by injection molding, compression molding, casting or thermoforming or blow molding. It is also .con-. templated that they could be formed of metal, such as thin spring metal stock, by forging, magniforming or impactforming and could have comparable resilience to the plastic blades described and be of the same generalshape. When made of metal, the weighted fin could be weldedin place. It could also be fabricated of thin wall shells with the blades formed in two concave shapes welded together at the edges and the weighted fin attached. 7 It is also contemplated that they could be made of laminated sheets built up to the desired shape, stacked together and bonded together by spot welding, cementing, soldering or any of the well known processes to provide a laminated structure.

It is apparent that the above invention enables a propeller to be constructed of a very simplified form as compared to the prior art. That there are no moving parts except that which occurs within the blades themselves. It is also contemplated that the structure enables a much closer approximation to the theoretical true pitch angle than heretofore has been known available in propellers. Such propellers made of corrosion resistant plastic will not deteriorate, regardless of the 'kind of water, and will not have the corrosion tendencies that are common with the prior art propellers.

Having thus described the invention in some embodiments thereof, it will be apparent to those versed in the art that numerous and extensive modifications as well as.

uses thereof may be made without departing from the spirit of the invention as pointed out in the appended claims.

I claim:

1. A propeller of the class described comprising a hub, at least one propeller blade extending from the hub and formed integrally therewith, said blade being of a material having limited flexibility and being resilient, a fin attached to the low pressure side of the blade and arranged to cause an increase in the pitch of the blade with an increase in r.p.m.

2. A propeller as described in claim 1, wherein said blade is held against rotation at the hub and has a low pitch extending away from the hub when the blade operates at a low r.p.m.

3. A propeller as described in claim 1, wherein the pitch of the blade becomes progressively less from the hub end of the blade toward the tip of the blade at zero r.p.m. and wherein said pitch becomes essentially constant throughout the length of the blade as said blade approaches design or cruising r.p.m.

4. A propeller as described in claim 1, wherein the increase in pitch of the blade with an increase in r.p.m. is brought about by water pressure acting on said fin.

5. A propeller as described in claim 1, wherein said blade has a radial axis with a larger surface area on the side of the axis away from the direction of rotation.

6. A propeller as described in claim 2, wherein said fin is provided with a weight disposed toward the trailing edge thereof and said fin and said blade are so designed that the blade flexes with r.p.m. to increase the pitch with increase in r.p.m. to attain substantially a true pitch.

7. A propeller as described in claim 6, wherein said fin is weighted at such a point that the centrifugal forces on the fin cause a distortional flexing of the blade with increase in r.p.m. to increase the pitch.

8. A propeller as described in claim 7, wherein said fin extends transversely across the blade in a curved line on a radius extending from the axis of the hub.

9. A propeller as described in claim 8, wherein said fin merges with the leading edge of the blade and extends outward from the blade at its trailing edge.

References Cited by the Examiner UNITED STATES PATENTS 1,798,299 3/1931 Antoni -l60.5 2,537,393 1/1951 Bisch et al 170160.5 X 2,791,281 5/1957 Boyd 170160.5 X

FOREIGN PATENTS 1,938 1876 Great Britain.

MARTIN P. SCHWADRON, Primary Examiner.

SAMUEL LEVINE, Examiner.

E. A. POWELL, 1a., Assistant Examiner. 

1. A PROPELLER OF THE CLASS DESCRIBED COMPRISING A HUB, AT LEAST ONE PROPELLER BLADE EXTENDING FROM THE HUB AND FORMED INTEGRALLY THEREWITH, SAID BLADE BEING OF A MATERIAL HAVING LIMITED FLEXIBILITY AND BEING RESILIENT, A FIN ATTACHED TO THE LOW PRESSURE SIDE OF THE BLADE AND ARRANGED TO CAUSE AN INCREASE IN THE PITCH OF THE BLADE WITH AN INCREASE IN R.P.M. 